Radiant gas burners



Oct. 6, 1964 E. RAVICH 3,151,659

' RADIANT GAS BURNERS Filed April 17, 1958 2 Sheets-Sheet 1 INVENTOR LEOMi/FO xawa/ BY p w w ATTORNEYS Oct. 6, 1964 L. E. RAVICH RADIANT GASBURNERS 2 Sheets-Sheet 2 Filed April 17, 19.58

INVENTOR lzo/wwfz wm ATTORNEYS United States Patent 3,151,659 RADIANTGAS BURWERS Leonard E. Ravich, Cleveland Heights, Ohio, assignor to HuppCorporation, Cleveland, Ohio, a corporation of Virginia Filed Apr. 17,1958, Ser. No. 729,153 7 Claims. (El. 153-116) This invention relates togas burners and more particularly to gas burners which have a radiationsurface rendered incandescent by the combustion of fuel on or adjacentthe surface.

One burner of this type is disclosed and claimed in United States Patent2,775,294. In this burner 21 gas-air mixture is fed to a distributingchamber, one wall of which is formed by a plurality of perforatedceramic blocks through which fuel and air mixture passes. Combustionoccurs on or adjacent the outer surface of the block or blocks andraises the temperature of the outer block surface to a level at whichenergy in the infra-red spectrum is emitted. The efficiency of burnersof this type is dependent to a large extent upon the temperature towhich the outer surface of the ceramic block is raised with a given gasinput since, as is well known, the emission of radiant energy increasesgeometrically with an increase in temperature of the radiating surface.

Many expedients have been suggested in the past to increase theefficiency of such burners and specifically to raise the temperature ofthe radiating surface without appreciably increasing the rate at whichfuel is supplied to the burner. One of these expedients involves thepositioning of a screen in front of the radiant surface of the blocks.Use of the screen has produced a substantial improvement in certainperformance characteristics of the burner by substantially raising thetemperature of the face of the burner blocks. However, the increase intemperature efiected by this prior construction is accompanied by theproduction by the burner of carbon monoxide in amounts which areconsiderably in excess of the limits established by the American GasAssociation for safe operation. The reason for the production of theexcessive amount of carbon monoxide in the prior burner has not beenfully known prior to the present invention. However it has now beendiscovered that the screen produces a slight back pressure which reducesthe amount of primary air available for combustion at the surface of thetile.

Accordingly, despite the increase in overall eficiency of the burnereffected by the installation of the screen and despite the otheradvantages which are to be derived from. the use of screens such asprotection of the burner blocks against mechanical damage, neverthelesssuch screens can be used only when the burners are installedout-of-doors or in other areas where the ventilation is sufhcient tomeet safety standards.

With the foregoing considerations in mind, it is a principal purpose andobject of the present invention to provide improved screen constructionsfor gas-fired radiant burners which are effective to overcome thedisadvantages of prior screen constructions by increasing the radiationefficiency without decreasing the combustion efficiency.

It is a further object of the present invention to provide novelgas-ired radiant burners, including novel screen constructions whicheffectively increase the radiant energy emitted by the burner for agiven gas input, which are completely safe and produce carbon monoxidein amounts which are Well below the limits set by the American GasAssociation for safe indoor operation.

It is a further and more specific object of the present invention toprovide improved screen constructions for radiant gas fired burners andmeans for detachably supporting the screens on the burners.

3,l5l,659 Federated Get. 6, 1964 "ice There are many applications whereit is desired to provide burners with a means of regulating theinfra-red radiant energy emission from the ceramic surface. A reductionof gas flow into the burner venturi by a valve will cause a decrease inceramic surface temperature with a resulting decrease in radiant energyemission. However, the decrease in gas flow will cause an accompanyingdecrease in air aspiration. An inefficient combustion reaction resultswith an increase in the carbon monoxide in the products of combustiongreater than accepted limits of toxicity. In accordance with a furtheraspect of the present invention, screen assemblies are provided at thefront face of the burner blocks along with a means for adjusting thespatial relationship of the screens and the burner face. The infra-redemissivity from the burner increases as the screen is set closer to theburner face and decreases as the screen is moved away from the burnerface. All this is accomplished without a change in input gas pressure,air aspiration, or an increase in carbon monoxide in the products ofcombustion.

Another object of the present invention is, therefore, to provideimproved gas fired radiant burners having a means for changing theposition of the screen assembly at the front burner face to render theburner capable of adjustment of infra-red emission.

In certain app ications where it is desired to operate the burners witha very high surface temperature, the radiant blocks become heated to thepoint where flashback may occur. In accordance with another aspect ofthe present invention, screen assemblies are provided at the rear faceof the blocks which receive heat from the rear face of the blocks anddissipate it through the burnerv housing thus maintaining thetemperature of the rear face of the radiant blocks at a point below thatat which flashback can occur.

It is thus a further object of the present invention to provide improvedgas-fired radiant burners having novel screen constructions positionedopposite each of the faces of the burner blocks to render the burnercapable of high temperature operation with an efiiciency and safety notheretofore obtainable.

Additional objects and advantages will become ap parent as thedescription proceeds in connection with the accompanying drawings inwhich:

FIGURE 1 is a front elevation of a burner constructed in accordance withthe present invention; and

FIGURE 2 is an end elevation of the burner of FIG- URE l; and

FIGURE 3 is an end elevation of the burner of FIG- URE 1 provided with ameans of screen adjustment; and

FIGURE 4 is a side elevation of the burner of FIG- URE 1 provided with ameans for screen adjustment; and

FIGURE 5 is a front elevation of a component of burner shown in FIGURES3 and 4 designed to provide two degrees of infra-red emissivity; and

FIGURE 6 is a front elevation of a component of burner shown in FIGURES3 and 4 designed to provide three degrees of infra-red emissivity.

As stated above, the main burner structure may be the same as thatdisclosed and claimed in Patent No. 2,775,294. Accordingly, the burnerwill be described herein only to the extent necessary to a fullunderstanding of the present invention, reference being had to theaforesaid Patent No, 2,775,294 for other details of construction.

The burner housing 2%) is metallic and is preferably of one-piece castconstruction and comprises bottom, side and end walls 22, 24, and 26respectively which enclose a distributing chamber 28 of generallyrectangular form. A boss 30 formed on one end of the housing carries afuel nozzle assembly 32 which is supplied with gas through a suitablesupply conduit 34. As more fully explained in Patent No. 2,775,294, thegas issuing through nozzle 32 entrains a flow of air which is deliveredto the interior of the chamber 28 formed by the walls 22, 24, and 26.The open top of the burner is closed by a plurality of burner blocks 36which are secured to the burner housing by screws 38. a

The blocks 36, which are preferably ceramic tiles, are provided with aplurality of small straight passages 40 through which the combustiblefuel-air mixture supplied to the distributing chamber passes. Combustionof the mixture occurs on or adjacent the outer surface of the blocks 36,heating the block surface rapidly to a temperature in the neighborhoodof 1550 F. at which temperature the surface of the tile becomesincandescent and emits energy in the infra-red spectrum. The outersurface of the tiles in the combustion area reaches its temperaturewithin a very short time and thereafter remains substantially at saidtemperature.

. It is known that the amount of infra-red energy propagated risessharply with an increase in the temperature of the outer surface of thetile, particularly above 00 F. In accordance with the present invention,a substantial increase in the equilibrium operating temperature 'isachieved by the provision of a novel screen construction extending overonly a part of the face of the burner.

In a preferred embodiment of the invention as shown in the drawings, thescreen construction consists of four identical screen strips 42 whichextend across the burner from side to side.- At their opposite ends thescreen strips 42 extend into inwardly facing U-shaped channel framemembers 44 which are mounted by machine screws 46 directly to thehousing member 20. The spacing between the channel frame members 44 andthe front face of the housing is determined by one or more hex-head nuts48. The screen strips 42 are held in place by cotterpins 50 which extendthrough the channel frame members 44. It will be noted that the screensleave a substantial portion of the radiant blocks uncovered. In atypical case the radiant blocks are 1%" wide and the screen strips are1" wide so that less than of the radiant blocks are covered. The screensare placed about from the burner face. a

A mechanical means for adjustment of distance between screens and burnerface is shown in FIGURE 3. Screens 42 extend across burner from side toside. At their opposite ends the screens 42 extend into inwardly facingU-shaped channel frame members 44 which are attached near each corner ofthe burner housing 20 by springs 56 and machine screws 58. Theminimumspacing-between the screens 42 in channel frame members 44 and the frontface of the housing 20 is determined by spacers 60. Well 62 in burnerhousing 20 permits the use of a longer spring without changing theminimum spacing between the screens and the burner block.

Spacers 64 are properly located on rod 66 so that one will rest onflange 68 of side 24 and the other will rest on the flange of side 26 ofburner member20. Rod 66 is of sufiicient length to extend about one halfinch beyond each spacer. The spacer and rod assembly is held in pla'ceby placing the ends of rod 66 into holes in brackets 70 which arefastened to the burner housing 20 by machine screws 72.

When sides B and B of spacers 64 are in contact with the flanges ofsides 24 and 26 and the lower surfaces of U-shaped channel frame members44, the screen will be spaced at an optimum distance from the burnerface and maximum emission for any given gas pressure will result. Whensides A and A of spacer 64 are in contact with the flanges and U-shapedchannels the screen will be spaced at a greater distance from the burnerface and a lower surface temperature results.

The spacers may be rotated by means of knob 74 affixed to end of rod 66.Springs 56 are in a stretched condition when sides A and A of spacer 64are used for adjusting screen height. a When spacer 64 is rotated thetension of springs 56 will pull the screen assembly down until channelframe members 44 and the flanges of burner housing 20 are in contactwith sides B and B' of spacer 64.

Preferred dimensions of spacer 64 are one half inch between sides B andB and one inch between sides A and A.

For a three position setting an arrangement such as spacer 76 can beemployed in the same manner as described for spacer 64. Preferreddimensions for spacer 76 are one inch between surfaces A and A,five-eighths inch between surfaces B and B and thirteen-sixteenths inchbetween surfaces C and C.

It has been demonstrated by actual tests that the utilization of partialscreen assemblies as described above substantially raises the surfacetemperature of the ceramic blocks and thus improves the overallefliciency of the burner while at the same time permitting combustion tocontinue with such efficiency that the percentage of carbon monoxideproduced is well within permissible limits. It has been found, forexample, that the surface temperature of the radiant blocks can beraised to the neighborhood of 2000 F. or higher and that the limitingfactor becomes the resistance of the blocks to deterioration at theserelatively elevated temperatures or the tendency toward flash-back. Inother cases where a very high surface temperature is not required, thenormal surface temperature of about 1600 F. can be maintained with asubstantially reduced supply of fuel.

The increase in the surface temperature of the radiant blocks isproduced by the fact that the screen absorbs a substantial amount ofheat energy from the hot products of combustion as well as from radiantenergy transfer from the incandescent ceramic surface to the screen. Ina short time the screen approaches the temperature of the ceramicsurface. As is well known, the rate of energy transfer or propagation isproportional to the difference in temperature between the transmitterand receiver. Since the screen functions as a receiver for at least alimited portion of the radiant blocks, the rate of energy transferredaway from the blocks in this area is substantially decreased and theportion of the block accordingly becomes substantially hotter. While thebody of the block at normal room temperature has a very low thermalconductivity, nevertheless the surface of the block at a temperature of1600 F. or higher has a very high thermal conductivity. The thermalconductivity is sufficiently high at the operating temperature that thecreation of hot spots behind the screen is avoided and the entiresurface of the tile assumes an equilibrium condition at which thetemperature of the surface of the tile is substantially uniform.

While the dimensions and configuration of the screen may be varied tosome extent, one screen which has worked very satisfactorily is aNichrome screen of 5 or 6 mesh placed at a distance of approximatelyfrom the outer surface of the radiant blocks.

Alte'rnately, a one-piece variable density screen may be used having arelatively fine mesh, for example 5 or 6' mesh, over the areas roughlyequivalent to the area covered by the screen strips 42 connected byareas of relatively coarse mesh. Such a screen would function in thesame manner as the separate strips but would afford additionalprotectionto the blocks.

The substantial increase in the temperature of the outer surface of theradiant blocks which is made possible by the use of screens of thepresent invention also increases to some extent the tendency of theblocks to flash-back. The invention also comprises novel means forreducing the tendency toward flash-back. In accordance with theinvention this is accomplished by utilization of a screen assemblyindicated generally at 52 which is spaced from and parallel to the rearface of the burner blocks 10. The screen may be of relatively fine meshand its mesh may be uniform. The screen is held in place by L-shapedstrips 54 which extend around the periphery of the screen and aresecurely attached to the inner surfaces of the walls of the housing 29in good heat exchange relation therewith. As indicated above, the rateof transmission or propagation of energy from one body to another isproportional to the difference in their temperatures. Since the screen52 is maintained at a relatively low temperature which is substantiallythat of the body of the housing 20, energy is transmitted rapidly fromthe rear surface of the radiant blocks to the screen. The rate oftransfer of energy is sufiiciently high so that the rear face of theburner blocks is maintained at a temperature well below the ignitionpoint of the combustible mixture and the danger of flash-back iseffectively eliminated.

From the foregoing it will be apparent that the above stated advantagesof the invention have been achieved by the provision of novel screenassemblies which substantially increase the radiating efiiciency ofradiant gas burners Without decreasing their combustion efficiency andin which the carbon monoxide produced by the burner is held well belowpermissible limits and in which the danger of flash-back is eflfectivelyeliminated.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is:

1. A gas burner comprising a housing having a chamber therein,perforated burner plate means forming a wall of said chamber, means forintroducing a fuel-air mixture into said chamber which passes throughthe perforations in said burner plate means and burns adjacent the outersurface thereof, frame members, means mounting said frame members inparallel spaced relation with the outer surface of said burner platemeans, means resiliently urging said frame members toward said surfaceof said burner plate means, adjustable means acting in opposition tosaid resilient means to determine the spacing between said frame membersand said surface of said burner plate means, and a plurality of separatewire mesh screen strips carried by said frame members in spaced relationto each other and being disposed in a single plane spaced from andsubstantially parallel to said burner plate means.

2. A gas burner comprising a housing having a chamber therein,perforated burner plate means forming a wall of said chamber, means forintroducing a fuel-air mixture into said chamber which passes throughthe perforations into said burner plate means and burns adjacent theouter surface thereof, frame members, means mounting said frame membersin parallel spaced relation with the outer surface of said burner platemeans, means resiliently urging said frame members toward said surfaceof said burner plate means, a plurality of blocks interposed betweensaid frame members and said burner housing, said blocks having pairs ofopposed side surfaces spaced different distances apart, means mountingsaid blocks for rotation about an axis parallel to the surface of saidburner plate means to selectively dispose different pairs of surfaces inengagement with said frame members and said burner housing, and wiremesh screen structure carried by said frame members and havingrelatively fine mesh portions opposite a portion only of said burnerplate means.

3. A gas burner according to claim 2 wherein said wire mesh screenstructure comprises a plurality of spaced separate screen strips.

4. A gas burner comprising a burner housing, fiat perforated burnermeans mounted in said housing to form a continuous wall thereof, theouter surface of said burner means becoming incandescent upon thecombustion of a fuel-air mixture thereon, a plurality of fiat, separatewire mesh screen strips, and means mounting said screen strips on saidburner housing to dispose said strips in a single plane adjacent saidouter surface of said fiat burner means and spaced from andsubstantially parallel to said outer surface of said flat burner means,said screen strips extending completely across said burner means, saidscreen strips being effective to raise the temperature of said outersurface of said burner means, and said screen strips being spaced apartfrom each other sufficiently to permit the flow of combustion productsaway from said outer surface of said burner means and maintain eflicientcombustion thereon.

5. The gas burner according to claim 4 wherein the spacing between saidburner strips and said outer surface of said burner means is not morethan about of an inch.

6. The gas burner according to claim 4 wherein the area of said screenstrips is about 60% of the area of said burner means.

7. The gas burner according to claim 4 wherein said screen strips areeach spaced not substantially more than 73 of an inch from said outersurface of said burner means and the area of said screen strips is notsubstantially more than 60% of the area of said burner means.

References Cited in the file of this patent UNITED STATES PATENTS994,599 Meran June 6, 1911 1,462,643 Kreutzer July 24, 1923 2,822,285Hayward Nov. 26, 1935 2,841,133 Schwank July 1, 1958 FOREIGN PATENTS526,728 Belgium Mar. 15, 1954 494,087 Great Britain Oct. 17, 1938744,980 Great Britain Feb. 15, 1956 521,503 Italy Mar. 29, 1955

4. A GAS BURNER COMPRISING A BURNER HOUSING, FLAT PERFORATED BURNERMEANS MOUNTED IN SAID HOUSING TO FORM A CONTINUOUS WALL THEREOF, THEOUTER SURFACE OF SAID BURNER MEANS BECOMING INCANDESCENT UPON THECOMBUSTION OF A FUEL-AIR MIXTURE THEREON, A PLURALITY OF FLAT, SEPARATEWIRE MESH SCREEN STRIPS, AND MEANS MOUNTING SAID SCREEN STRIPS ON SAIDBURNER HOUSING TO DISPOSE SAID STRIPS IN A SINGLE PLANE ADJACENT SAIDOUTER SURFACE OF SAID FLAT BURNER MEANS AND SPACED FROM ANDSUBSTANTIALLY PARALLEL TO SAID OUTER SURFACE OF SAID FLAT BURNER MEANS,SAID SCREEN STRIPS EXTENDING COMPLETELY ACROSS SAID BURNER MEANS, SAIDSCREEN STRIPS BEING EFFECTIVE TO RAISE THE TEMPERATURE OF SAID OUTERSURFACE OF SAID BURNER MEANS, AND SAID SCREEN STRIPS BEING SPACED APARTFROM EACH OTHER SUFFICIENTLY TO PERMIT THE FLOW OF COMBUSTION PRODUCTSAWAY FROM SAID OUTER SURFACE OF SAID BURNER MEANS AND MAINTAIN EFFICIENTCOMBUSTION THEREON.